Tohatsu 3.5 B2 Idle Issue

[Sea Rider]

Hello again TG :

This is a special for you : have a brand new Tohatsu 3.5 B2-2 strokes. When engine has warmed enough at start position and throttle is lowered to minimum 1300 rpm the engine tends to shut off, if adjusted to 1500 rpm, won't shut off, but when engaged to forward the engine cliks & jumps a bit, when passed to neutral engine rpm's is a bit accelerated and does not lower to idle speed as when factory adjusted to 1300 rpm (turtle position)

When engine is adjusted to 1500 rpm in neutral, and full choke is activated, the engine doesn't do a thing, is it supposed to stall the engine and shut off ? What needs to be checked ? Please advise.

1-There is air leakage through carb body and manifold intake, probably carb metal band is not well adjusted or loose. Check carb big O ring ?

2-Engine block mating surfaces not well sealed, air leak

3-Probably jet needle clip is not adjusted in second position and is in 3rd slot towards lean adjustment

4-Check gas filter for obstruction, clean dirt, clean whole carb and inspect ?

Happy Boating

 

[TOHATSU GURU]

Re: Tohatsu 3.5 B2 Idle Issue

All of those things could potentially be a problem...But in the end it will almost certainly be a defective carb body requiring the replacement of the carburetor itself. I had a new 3.5 engine back in 05 that did the same thing. We played with the carb, adjusting and trying different component parts in it to no effect. Theory was that the body itself was miss cast allowing the engine to suck in too little fuel at an idle to run. Regardless, since the carburetor is inexpensive, it's going to be cheaper to replace it rather than spending any time working on it.

 

[Sea Rider]

Re: Tohatsu 3.5 B2 Idle Issue

Hello TG

Thanks for the data, will re check the carb/engine once 5 hour break in has ended, find strange about carb mis cast, bought (15) 3.5 B", were factory made new about 4 months ago for J-24 use, all of them are idling perfect. So will asume all parts are of latest 09 manufacturing.

Have noticed when placing a tiny tach to measure idle rpm that some of them are comming factory adjusted to 1350 rpm, some at 1500 in idle, would it be better to adjust all engines to 1350 rpm, so to have 1100 rpm when in forward gear. As long as the gear doesn't jump and have constant (not erratic) water pee exit, will there too much difference if adjusted to 1350 or 1500 rpm ? What are your thoughts ?

Understand that a digital tacho is a bit erratic (50-80 rpm) when reading, compared to a analog tacho in which the needle looks more steady.

Happy Boating

 

[TOHATSU GURU]

Re: Tohatsu 3.5 B2 Idle Issue

Depends on the load. On a dinghy, 1100 to 1125. On a sailboat, 1125 to 1150. I wouldn't worry about adjusting in neutral as keeping it running when dropped into gear is the critical thing.

 

[mmccoy555]

Re: Tohatsu 3.5 B2 Idle Issue

I would attempt a good carb cleaning before anything. A clogged low speed jet would cause the same thing.